Abrasion-resistant fluoropolymer mixtures

ABSTRACT

An abrasion-resistant fluoropolymer mixture comprising 
     (A) from 75 to 99% by weight of a fluorocarbon polymer 
     (B) from 1 to 25% by weight of an oxidized polyarylene sulfide and, based on the sum (A)+(B), 
     (C) from 0 to 15% by weight of a filler, 
     is used for the production of feed pipes for Bowden cables which are pressure-resistant and abrasion-resistant.

This application is a divisional application of Ser. No. 08/824,340which was filed Mar. 26, 1997 now U.S. Pat. No. 5,750,221 which is adivisional application of Ser. No. 08/475,077 filed Jun. 7, 1995 nowabandoned, which is a divisional application of Ser. No. 08/271,848filed Jun. 7, 1994 now abandoned.

The invention relates to highly effective, abrasion-resistant polymercompositions based on fluorocarbon polymers having considerably improvedlong-term properties, in particular for antifriction tubes, for examplefeed pipes for Bowden cables. They are prepared from mixtures offluoropolymers, for example polytetra fluoroethylene (PTFE) and oxidizedpolyarylene sulfides.

Fluoropolymers have been known for some time. They are distinguished byhigh heat resistance and excellent chemicals resistance. In addition tothe high toughness, both the thermoplastic and the non-thermoplasticfluoropolymers have a pronounced tendency to creep. In addition, thetribological properties of fluoropolymers are inadequate in manyapplications.

The literature describes additives, for example based on polyestercompounds, which either improve the tendency to creep or the abrasion offluoropolymers (JP-A 58/019397). However, they have the followingdisadvantages:

1. The polyester compounds decompose at the processing temperatures ofthe fluoropolymers,

2. the poor grindability of their mixture results in poorhomogenization, and

3. the addition of the additives known hitherto considerably decreasesthe chemicals resistance of the fluoropolymers.

The latter also applies to aromatic polysulfones, as described in theliterature (DE-A 24 18 282, JP-A-60/038465). In these cases, polymersare mentioned which are soluble in known organic solvents such asdimethylformamide or dichloromethane.

Also known is a curable mixture of hydrogen peroxide-treatedpolyphenylene sulfide and a pigment; this mixture contains 13% ofpolytetrafluoroethylene (U.S. Pat. No. 3,948,865). It is used forcrack-free coating of aluminum which coating can be cured in a shorttime. In this case, the polytetrafluoroethylene functions only asfiller.

Also known are tubular products which comprise mixtures ofpolytetrafluoroethylene and a polyarylene sulfide and, if desired,fillers and which have excellent sliding and friction properties (U.S.Pat. No. 4,362,069). For paste extrusion and as a polymer additive,preference is given to PTFE polymers containing from about 5 to 25% byweight of linear or branched poly-p-phenylene sulfide. The disadvantagesof these mixtures are the low chemicals resistance, the limited abrasionbehavior and the poor heat resistance of the polyarylene sulfidesemployed.

The object was therefore to develop fluoropolymer-based compositions ofparticularly low abrasion which do not have the disadvantages describedin the prior art or which have superior properties to those described.

The invention therefore relates to extruded tubular products whichcomprise a mixture of

(A) from 75 to 99% by weight of a fluorocarbon polymer and

(B) from 1 to 25% by weight of an oxidized polyarylene sulfide and,based on the sum (A)+(B),

(C) from 0 to 15% by weight of a filler and which, owing to theparticularly low abrasion, have a very long service life. Their use thusbrings economic advantages with respect to saving of material employedand durability.

It was surprising that the addition of oxidized polyarylene sulfides,for example polyarylene sulfones and/or polyarylene sulfide copolymerscontaining any desired proportions of oxidized sulfide groups, forexample S/SO/SO₂ -arylene copolymers, to thermoplastic ornon-thermoplastic fluoropolymers improves the tendency to creep and theabrasion while substantially retaining the chemicals resistance and heatresistance. Furthermore, polymer mixtures of this type are distinguishedby very good mechanical properties in the tensile test. These mixturesare particularly suitable for applications in the form of extrudedtubes, as used for sheathing Bowden cables.

According to the invention, it is possible to use the followingfluorothermoplastics containing recurring units of formula (I): ##STR1##where X is O--R, where R is a perfluorinated alkyl radical having 1 to 8carbon atoms, and m and n are each a number from 0.01 to 1, where thesum of m and n is 1.

The mixtures can furthermore contain fluorothermoplastics containingrecurring units of the formulae (II)-(IV):

    --(CF.sub.2 --CF.sub.2).sub.m --(CH.sub.2 --CH.sub.2).sub.n --(II)

    --(CF.sub.2 --CF(CF.sub.3)).sub.m --(CF.sub.2 --CF.sub.2).sub.n --(III)

    --(CF.sub.2 --C (Cl) F).sub.m --(CH.sub.2 --CH.sub.2).sub.n --(IV)

in which m and n are as defined above, and recurring units of theformulae (V) and (VI): ##STR2##

Also suitable for the mixtures according to the invention arenon-thermoplastic fluoropolymers containing structural units of thefollowing formulae: ##STR3##

It has proven advantageous to use polytetrafluorothylenes in powder formwhich are suitable for paste extrusion.

Polymers which can be used for the mixtures according to the inventionare linear and branched polyarylenes (Mw: 4000-200 000) whose recurringunits contain at least one S and/or SO and/or S₂ group as bridge andwhich have a heat resistance which is adequate for the fluoropolymersemployed in each case, i.e. the two polymers in the mixture are stableunder processing conditions. The polyarylenes have the formula (IX)

    -- (Ar.sup.1).sub.d --X!.sub.e -- (Ar.sup.2).sub.i --Y!.sub.j -- (Ar.sup.3).sub.k --Z!.sub.l -- (Ar.sup.4).sub.o --W!.sub.p --(IX)

in which each Ar¹, Ar², Ar³, Ar⁴, W, X, Y and Z, independently of theothers, is identical to or different from the others. The indices d, e,i, j, k, l, o and p are, independently of one another, zero or integers1, 2, 3 or 4, where their sum must be at least 2. Ar¹, Ar², Ar³ and Ar⁴in the formula (IX) are simple or directly para-, meta- or ortho-linkedarylene systems having 6 to 18 carbon atoms, W, X, Y and Z are linkinggroups selected from --SO₂ --, --S--, --SO--, --CO--, --CO₂ --, alkyleneor alkylidene groups, each having 1-6 carbon atoms, and --NR¹ --groupswhere R¹ is an alkyl or alkylidene group having 1-6 carbon atoms.Excluded from this group are polymers from the class consisting of thepolyether sulfones.

Particularly suitable polymers are polyarylenes containing recurringunits of the formula (X):

     --(S--E).sub.a --(--SO--E).sub.b --(SO.sub.2 --E).sub.c --!(X)

in which each E, independently of the others, is phenylene, naphthyleneor biphenylene, b and c, independently of one another, have values offrom 0 to 1 and a has values of from 0 to less than 1, with the provisothat the sum a+b+c is equal to 1 and at least two of the indices aregreater than zero and if any sulfur links (--S--) are present, at leastfurther --SO-- and --SO₂ -- links are also present.

Polymers which can be specifically employed are those containingrecurring units of formulae (XI)-(XIII) ##STR4## and oxidizedpolyphenylene sulfides containing recurring units of the formula (XIV)##STR5## where the sulfone content is at least 65%.

The oxidized polyarylene sulfides are prepared by the processesdescribed in (as yet unpublished) German patent applications P 43 14737.2 which corresponds to U.S. Ser. No. 08/237,271, and P 43 14 738.0which corresponds to U.S. Ser. No. 08/237,272 of 4 May 1993, which areexpressly incorporated herein by way of reference.

The particle size of the oxidized polyarylene sulfides according to theinvention is generally from 3·10⁻⁶ to 300·10⁻⁶ m, preferably from 5·10⁻⁶to 100·10⁻⁶ m, in particular from 5·10⁻⁶ to 50·10⁻⁶ m.

The proportion of polyarylene sulfones or S/SO/SO₂ -arylene copolymersis, according to the invention, 1 to 25% by weight, preferably from 1.5to 20% by weight, in particular from 2 to 15% by weight. The proportionof fluoropolymers in the mixtures according to the invention is from 75to 99% by weight, preferably from 80 to 98.5% by weight, in particularfrom 85 to 98% by weight, where the proportions of the two polymers,based on the entire polymer mixture, add up to 100%. The mixturesaccording to the invention can contain one or more fluoropolymers andone or more polyarylene sulfones and/or S/SO/SO₂ -arylene copolymers andmodified fluoropolymers, modified polyarylene sulfones or modifiedS/SO/SO₂ -arylene copolymers.

According to the invention, the mixtures can additionally contain up to15% by weight, based on the total amount of polymer mixture, of fillers.These comprise glass, for example glass microbeads, metal or mineralproducts, which can be in various forms.

In the preparation of the molded products, the mixture according to theinvention is prepared by two methods. In the first method (a), afluoropolymer in powder form is mixed with all of the oxidizedpolyarylene sulfide to be employed in a mixer in which the particlesmust not be subjected to any shear forces, for example in a tumblemixer. After adequate prefixing, a lubricant, for example a hydrocarbonmixture such as Shellsol 100-140 (producer Shell AG, Hamburg, Germany),is added, and the mixture is treated further until homogeneous.

In a further method (b), the oxidized polyarylene sulfide is added to adispersion of the fluoropolymer. By subsequent extraction by stirring,the two polymers are deposited as a mixture. The deposited polymermixture is then mixed with a lubricant as in method (a).

The resultant mixtures of components (A), (B) and, if used, (C) areprecompacted (compaction ratio 1:3) and subsequently molded by pasteextrusion to give a cylindrical hollow shape or a tube. This preformproduced in this way is then subjected to two-step thermal treatment. Inthe first step, the lubricant is removed at from 100° to 350° C., andthe molding which remains is subsequently sintered at temperatures offrom 260° to 470° C. for from 10 seconds to 20 minutes. If desired, thiscan be followed by thermal aftertreatment at from 260° to 470° C. forfrom 5 minutes to 24 hours.

EXAMPLES

1) Mixture A':

A dry mix comprising 93 parts by weight PTFE (™Hostaflon TF 2071,Hoechst AG, Frankfurt/Main, Germany) 7 and parts by weight ofpolyphenylene sulfone (prepared as described in the German patentapplication 43 14 738.0) was prepared. As lubricant, 20 parts by weightof Shellsol 100-140 were added per 100 parts by weight of PTFE.

2) Mixture B' (comparative example):

93 parts by weight of PTFE (as in mixture A') and 7 parts by weightpolyphenylene sulfide. Lubricant addition as for mixture A'.

Mixtures A' and B' containing the lubricant were converted into tubes inan extruder, type WP 80/1000, year cf construction 1991 (Worek,Adelsdorf-Neuhaus, Germany).

Machine and processing data:

Barrel: 63.5 mm internal diameter

Mandrel: 19.0 mm external diameter

Extrusion die: 7.0 mm internal diameter

Extrusion mandrel: 4.0 mm external diameter

Reduction ratio (RR): 111

Die temperature: 30° C.

Barrel temperature: 30° C.

Drying zone temperature: 290° C.

Sintering zone temperature: 450° C.

Extrusion rate: 0.7 m/min

Extrusion pressure mixture A': 135 bar

Extrusion pressure mixture B': 125 bar

The extruded tubes had the following final dimensions:

Internal diameter: 3.2 mm

External diameter: 6.5 mm

Shrinkage of external diameter: 7.1%

The abrasion of the tubes made from mixture A' and mixture B' wassubsequently determined by the "Bowden cable methods":

In this, a tube was shaped into a quarter circle (tube radius 120 mm) ineach of 2 devices. Of these 2 devices, one is in a drying cabinet(experiments at elevated temperatures, here: 150° C.) and the other isin a normal environment (experiments at RT). A steel cable weighted ateach of its ends with a mass of 60 kg runs in the tubes in both devices.This steel cable (diameter 3 mm, 19 strands of 0.6 mm each) is movedalternately in both directions by 40 mm in each case (stroke length) bymeans of a cylinder (frequency: 60 strokes/min), so that frictioncontact occurs between the tube and the steel cable. The weight loss ofthe tubes after a certain number of strokes is measured, both at roomtemperature and at the set heating cabinet temperature (150° C.).

    ______________________________________                 Abrasion  %! after                            Abrasion  %! after                 0.5 million strokes                            1.0 million strokes    Examples 1 and 2                   at RT   at 150° C.                                    at RT at 150° C.    ______________________________________    Tube made from mixture A'                   0.3     1.0      0.7   2.1    Tube made from mixture B'                    2.0*    2.8*    --    --    (comparison)    ______________________________________     *Rubbed through after 30,000 strokes; abrasion determined after 30,000     strokes.

3) In addition, tubes of smaller diameter than above were extruded frommixtures A' and B' and further mechanical properties were determinedthereon. These tubes were produced on a Davis electric cable extruder(Davis electric type: 0-001-796, Wallingford, Conn., USA).

    ______________________________________    Machine and processing data:    Barrel:            50.8 mm internal diameter    Mandrel:           12.7 mm external diameter    Extrusion die:     3.35 mm internal diameter    Extrusion mandrel: 2.45 mm external diameter    Reduction ratio (RR):                       463    Die temperature:   50° C.    Barrel temperature:                       40° C.    Drying zone temperature:                       150° C.    Sintering zone temperature:                       400° C.    Extrusion rate:    4 m/min    Extrusion pressure mixture A':                       530 bar    Extrusion pressure mixture B':                       380 bar    The extruded tubes had the following final dimensions:    Internal diameter: 2.0 mm    External diameter: 2.9 mm    Shrinkage of external diameter:                       13.4%    ______________________________________

Tensile tests were carried out on the two tubes:

    ______________________________________                Tear strength  %!                          Elongation at break  %!    Examples 3 and 4                  at RT  at 200° C.                                  at RT  at 200° C.    ______________________________________    Tube made from mixture A'                  94     28       440    210    Tube made from mixture B'                  96     27       410    190    (comparison)    ______________________________________

We claim:
 1. A cable comprising an extruded tube and a metal cablewithin the extruded tube, wherein the cable can be moved within the tubeand is provided with a lubricant, wherein the sheath of the metal cableis an extruded tube made from an abrasion-resistant fluoropolymermixture comprising(A) from 75 to 99% by weight of a fluorocarbonpolymer, (B) from 1 to 25% of an oxidized polyarylene sulfide and, basedon the sum (A)+(B), (C) from 0 to 15% by weight of a filler.
 2. Thecable as claimed in claim 1, wherein component B is an oxidizingpolyarylene sulfide which is a linear or branched polyarylene systemcontaining recurring units of the formula

    {(Ar.sup.1).sub.d --X}e{(Ar.sup.2).sub.i --Y}j{Ar.sup.3).sub.k --Z}.sub.i {(Ar.sup.4).sub.o --W}p--                                 (IX) wherein,

the indices n, m, i, j, k, l, o and p are identical or different and areintegers from 0 to 4, where their sum must be at least 2, Ar¹, Ar², Ar³and Ar⁴, are identical or different and are simple or directly para-,meta- or ortho-linked arylene systems having 6 to 18 carbon atoms, andW, X, Y and Z are identical or different and are linking groups selectedfrom --SO₂ --, --S--, --SO--, --CO--, --CO₂ --, alkyl or alkylidenegroups having 1-6 carbon atoms, with the proviso that component (B)contains at least one SO or SO₂ group polymers from the class consistingof polyether sulfones being excluded.
 3. The cable as claimed in claim1, wherein the fluorocarbon polymer is polytetrafluoroethylene.
 4. Thecable as claimed in claim 2, wherein the fluorocarbon polymer ispolytetrafluoroethylene.
 5. The cable as claimed in claim 1, wherein theoxidized polyarylene sulfide is a polyarylene sulfone, apolyarylenesulfide/sulfoxide/sulfone copolymer, or a mixture thereof. 6.The cable as claimed in claim 1, wherein constituent (B) is present inan amount from 1.5 to 20% by weight, and is a polyarylene sulfone, apolyarylenesulfide/sulfoxide/sulfone copolymer, or mixtures thereof. 7.The cable as claimed in claim 1, wherein constituent (B) is apolyarylene containing recurring units of the formula

    {--(S--E--).sub.a --(--SO--E).sub.b --(SO.sub.2 --E).sub.c --}(X)

in which E, independently of the others, is phenylene, naphthylene orbiphenylene, b and c, independently of one another, having values offrom greater than 0 to 1, and a has values of from 0 to less than 1,with the proviso that the sum a+b+c is equal to 1, and if any sulfurlinks (--S--) are present, at least further --S-- and --SO₂ -- links arealso present.
 8. The cable as claimed in claim 1, wherein constituent(B) is a polyphenylene sulfone containing recurring units of theformulae ##STR6## ##STR7##
 9. The cable as claimed in claim 1, whereinconstituent (B) is an oxidized polyphenylene sulfide of the formula##STR8## in which at least 65% of the sulfur atoms have been oxidized tosulfone groups.
 10. The cable as claimed in claim 1, wherein theparticle size of the oxidized polyarylene sulfides is from 3·10⁻⁶ m to300·10 m.
 11. The cable as claimed in claim 1, wherein the fillercontent is from 5 to 13% by weight.
 12. The cable as claimed in claim 1,comprising from 85 to 98% by weight of polytetrafluoroethylene and from2 to 15% by weight of polyphenylene sulfone.
 13. The cable as claimed inclaim 1, wherein said fluorocopolymer mixture comprises from 85 to 98%by weight of polytetrafluoroethylene and from 2 to 15% by weight ofpolyphenylene sulfide/sulfoxide/sulfone copolymers.